Cohesive strength, definition

Tensile properties of the HDPE/RET blend are shown in Table 8.2. The HDPE 100/0 carbon-fibre composite showed complete linear stress-strain behaviour up to its ultimate tensile strength and fracture at 10.3% strain. No definitive fracture was seen in the HDPE blends. This is due to the interfacial de-bonding between the constituents within the polymer. The apparent loss of cohesive strength of the matrix material resulted in fibre pull-out and interlaminar slip between the carbon-fibre plies. 

Thermodynamic Properties The variation in solvent strength of a supercritical fluid From gaslike to hquidlike values may oe described qualitatively in terms of the density, p, or the solubihty parameter, 6 (square root of the cohesive energy density). It is shown For gaseous, hquid, and SCF CO9 as a function of pressure in Fig. 22-17 according to the rigorous thermodynamic definition ... 

Hardness is a somewhat ambiguous property. A dictionary definition is that it is a property of something that is not easily penetrated, spread, or scratched. These behaviors involve very different physical mechanisms. The first relates to elastic stiffness, the second to plastic deformation, and the third to fracturing. But, for many substances, the mechanisms of these are closely related because they all involve the strength of chemical bonding (cohesion). Thus discussion of the mechanism for one case may provide some understanding of all three. 

Adhesives are nonmetaUic substances used to join two surfaces by means of surface adherence (adhesion) and inherent strength (cohesion), DIN 16920. This definition of adhesives does not cover water glass adhesives, adhesive ceramics, or adhesive mortars. The substances used as adhesives are polymers that go through a liquid phase at least once (reactive adhesives) or more than once (hotmelts, thermally activated adhesives). The liquid phase can also be achieved by dissolution in suitable solvents (nonreactive adhesives). In dispersion adhesives, the polymer molecules are dispersed (finely distributed) in a liquid - usually water - whereby the polymer molecules themselves are not dissolved. Fig. 6. These adhesives are also known as water-based or aqueous adhesives. It must be remembered that solvents are contained in these adhesives in addition to the water. Genuine aqueous adhesives contain less than 5% solvents in the liquid phase. The dispersions crnitain, in contrast to the solute adhesive molecules, additional substances, disposal of which requires specific additional measures. Since the dispersions represent stable systems in water, the water-resistance of such adhesives is reduced. Their thermal and water resistance can be increased by additional crosslinking (usually with isocyanates). 

It is possible to perform a physical analysis to predict either liquid lens or thick him formation, and the strength of adhesion between the two phases. In order to assess the adhesion strength, initially we need to formulate the work of cohesion and adhesion. In Section 2.1, we dehned the term cohesion to describe the physical interactions between the same types of molecule, so that it is a measure of how hard it is to pull a liquid (and solid) apart. In Section 3.5.3, we dehned, the work of cohesion, W), as the reversible work, per unit area, required to break a column of a liquid (or solid) into two parts, creating two new equilibrium surfaces, and separating them to inhnite distance. (In practice, a distance of a few micrometers is sufficient.) The work of cohesion required to separate liquid layers into two parts having unit area can obviously be expressed from the definition of surface tension as... 

There is a much interest as the strength of C-S-H is concerned, because the properties of paste and concrete are strongly affected by this component. Taylor [63], considering the properties of C-S-H, relates to the definition of gel as a dispersion system in which the attracting forces (cohesion) among its dispersed elements are so strong that all the system reveals a rigid network and, at low stress it behaves as an elastic body. 

Adhesion, by its definition, depends on the ability of two unlike phases to hold themselves together across a common interface. Physical adhesion must first take place before any other bonding processes such as chemical reaction can occur, and such physical adhesion depends on the strength of intermolecular force interaction, on the area of contact and on the distance separating the atoms forming the top layer of each surface (see Dispersion forces, polar forces). When both phases are undeformable, such as with two solids that are not atomically smooth, poor adhesion results because an insufficient area of each surface is in atomic contact with the other. When one phase is deformable, such as with a liquid of low viscosity, physical adhesion takes place at all parts of the surface. Physical adhesion with a liquid in contact with a solid leads to spreading and wetting processes that now depend on the competition of adhesion forces with cohesion forces within the liquid. 

Skills in assessing the behaviour and properties of soils require distinctions between total and effective stress and between drained and undrained loading together with basic definitions of strength, stiffness, friction, cohesion and so on. 

Yokoyama et al. (1982) measured the tensile strength with the swing method of the Hosokawa cohetester, for a range of particle sizes (1-90 urn) of different densities (0.928-6.01 g/cm ) over a range of moisture percentages (0.06-15.2% w/w), to evaluate the potential floodability of powders. Yokoyama et al. defined their dimensionless floodability, as opposed to Carr s definition of flowability, as the ratio of the cohesive force (C) - measured by cohetester - to the gravity force on particles m g). 

Per definition, only the tensile strength oz and no inclination depends directly on the consolidation pre-histoiy obtained from a Taylor series linearisation of the yield locus [28] near Mohr circle of cohesive stationary flow, see Eq.( 9). Now the simplest formulation of the linear yield locus dependent on radius (Jvr ( R,st and center stresses (average pressure in the powder) ctvm [Pg.78]

Two species combine to form a complex in water if the sum of the intermolecular forces between them more than olfsets the sum of the loss of favorable interactions with solvent and any unfavorable interactions that develop between solutes during complex formation. Collectively the interactions between non-bonded species are referred to as cohesive forces, defined as those forces lost when the species are transferred to infinite separation in the gas phase. While it is common to classify chemical forces as covalent or non-covalent, the interactions are fundamentally the same only the magnitude of the interactions varies. Cohesive, non-specific forces are weak compared to covalent interactions typically we consider cohesive forces as those forces with strengths less than 1% of covalent bond strengths. We will see, however, that this definition is somewhat arbitrary and in fact a continuum of interaction energies exists. 

The transition of a liquid phase to its vapor phase involves the separation of molecules in the liquid and the removal of molecules from the surface of the liquid into the vapor phase. The energy absorbed when a definite quantity of a liquid is vaporized (the latent heat of vaporization) therefore depends on the intermolec-ular attractive forces which have to be overcome in order to separate molecules. According to Trouton s rule, the boiling points of nonassociated liquids, on the absolute-temperature scale, are approximately proportional to their latent heats of vaporization. Hence, the boiling point of a liquid depends on the relative strength of cohesive intermolecular forces. 

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